Transmitter and transmitting method increasing the flexibility of code assignment

ABSTRACT

According to the present invention a transmitter and a transmitting method for communicating data symbols over a communication channel, for example, according to the CDMA system is presented. The transmitter ( 24, 25 ) comprises means ( 9 ) for spreading each data symbol with a respective spreading code, wherein the spreading codes are mutually orthogonal. Means ( 10 ) for scrambling are provided to scramble each spread symbol with a respective scrambling code, the scrambling codes respectively having the same length as the spreading codes. Furthermore, means ( 11 ) for the transmission of the spread and scrambled symbols are provided. According to the present invention the means ( 10 ) for scrambling are provided with a plurality of different scrambling codes, which can be used simultaneously within the same link.

This is a continuation of reissue continuation application Ser. No.12/537,563, filed Aug. 7, 2009; which is a reissue continuation ofreissue application Ser. No. 11/139,004, filed May 26, 2005 (now, U.S.Pat. No. Re. 41,025), which is a reissue of U.S. Pat. No. 6,570,889,issued May 27, 2003.

The present invention relates to a transmitter, a wireless transmissionsystem as well as to a method for the transmission of data symbols overa communication channel which particularly finds its application in thefield of so-called CDMA systems.

CDMA (Code Division Multiple Access) transmitting systems are known fromthe state of the art. According to one CDMA technique, after themodulation (symbol mapping), the symbols are spread by a so-calledspreading sequence or spreading code. After spreading the resulting datastream is scrambled by a scrambling sequence of a scrambling code. Thethus resulting data stream, which has been spread and scrambled, is thenpower-amplified and sent over a communication channel. The reverseprocedure happens at the receiving side.

In FIG. 3 an example for a transmission system comprising scrambling andspreading is shown. In the example of FIG. 3 only the downlinkcommunication channel 26 from a base station 24 to a mobile station 25is shown. The downlink 26 can comprise different channels D₁, . . . ,D_(N). Each channel comprises channelisation (spreading) 28, 30 andscrambling 29, 31. According to the state of the art in one link, as forexample the downlink 26 as shown in FIG. 3, only one scrambling sequence(scrambling code) and several different spreading codes (often referredto as channelization codes) are used depending upon the data rate andservices required. The drawback of this approach is that only certaintypes of channelisation codes can be used together and the highest datarate is constrained by the length of the shortest channelisation code.This is especially true when codes of different rates are used.

From WO96/05668 A1 and EP-A-565 506 techniques for multiple accesscoding for radio communication is known. According to these documentsinformation symbols are spread using orthogonal or bi-orthogonalcodewords. This spread information symbols are assigned a uniquescramble mask that is taken from a set of scramble masks having selectedcorrelation properties. The set of scramble masks is selected such thatthe correlation between the modulo-2 sum of two scramble masks with anycodeword is a constant magnitude independent of the codeword and theindividual mask being compared. According to one embodiment of WO96/05668 A1, when any two masks are summed using modulo-2 sumarithmetic, the Walsh transformation of that sum results in a maximallyflat Walsh spectrum. For cellular radio telephone systems usingsubtractive CDMA demodulation techniques, a two-tier ciphering systemensures security at the cellular system level by using a pseudorandomlygenerated code key to select one of the scramble masks common to all ofthe mobile stations in a particular cell. As according to thesetechniques one common scramble mask is used for all mobile stations in aparticular cell, the above-cited drawback arises that only certain typesof channelisation codes can be used together limiting the number ofavailable channelisation (spreading) codes.

In view of the above-cited drawbacks it is of the object of the presentinvention to enhance the flexibility of code assignment for a CDMAsystem, particularly within a cell sector and/or to increase the maximumdata rate.

The central idea of the present invention thereby is a new codeallocation scheme for a CDMA system utilising two or more scramblingcodes within one link (uplink or downlink).

According to the present invention therefore a transmitter forcommunicating data symbols over a communication channel is provided, thetransmitter comprising means for spreading each data symbol with arespective spreading code, wherein the spreading codes are mutuallyorthogonal. Furthermore means for scrambling each spread symbol with arespective scrambling code are provided, the scrambling codesrespectively having the same length as the spreading codes. Means areprovided for the transmission of the spread and scrambled symbols.According to the present invention the means for scrambling are providedwith a plurality of different scrambling codes which can be usedsimultaneously within the same link.

The means for scrambling the spread symbols can use different scramblingcodes for an uplink communication channel and a downlink communicationchannel.

The spreading codes can be obtained by means of a code tree.

According to an aspect of the present invention, only in a downlinkcommunication channel different scrambling codes are used, wherein in anuplink channel only one scrambling code is used.

The means for scrambling can use different scrambling codes within thesame link only for channels demanding a high bit rate.

According to the present invention, furthermore a wireless transmissionsystem comprising a transmitter of the above-cited type is provided,wherein a subset of scrambling codes is respectively allocated to a cellof the transmission system.

Different spreading codes can be allocated to adjacent cells of thetransmission system.

According to the present invention, furthermore a method for thetransmission of data symbols over a communication channel is provided.Data symbols are spread with a respective spreading code, wherein therespective spreading codes are mutually orthogonal. Each spread symbolis scrambled with a respective scrambling code, the scrambling codes notchanging the band rate of the transmission (in contrast to the spreadingcodes). The spread and scrambled symbols are transmitted.

According to the present invention, when scrambling a plurality ofdifferent scrambling codes can be used, which are to be usedsimultaneously within the same link.

In the step of scrambling different scrambling codes can be used for anuplink communication channel and a downlink communication channel,respectively.

The spreading codes can be obtained by means of a code tree.

As an aspect of the present invention, only in a downlink communicationchannel different scrambling codes are used. In the uplink communicationchannel only one scrambling code is used, as the bit rate usually isless than in the downlink communication channel.

Different scrambling codes can be used within the same link only forchannels demanding a high bit rate.

Particularly different scrambling codes within the same link can be usedfor example for video channels and/or data channels, but for example notfor voice channels.

Further aspects, advantages and features of the present invention willnow be explained by means of embodiments of the present invention andwith reference to the enclosed figures of the drawings.

FIG. 1 shows a general view of a wireless transmission system accordingto the present invention,

FIG. 2 shows the spreading and scrambling according to the presentinvention respectively for a downlink communication channel and a uplinkcommunication channel between a base station and a mobile station of thewireless transmission station as shown in FIG. 1,

FIG. 3 shows the channelisation (spreading) and scrambling in a downlinkcommunication channel between a base station and a mobile stationaccording to the prior art,

FIG. 4 shows the plurality of cells in the transmission system accordingto the present invention,

FIG. 5 shows an application of the present invention to provide forflexible code allocation in CDMA systems, and

FIG. 6 shows an application of the present invention to provide forhigher data rate services.

A transmission system according to the present invention will now beexplained generally with reference to FIG. 1. As shown in FIG. 1,different data can be transmitted in a wireless manner. The data to betransmitted can comprise voice data from a telephone 1, 23, video data,for example, from a video camera 5 to be transmitted to a monitor 20 andother information data, as for example, data from a computer 6 to betransmitted to another computer 19. The analog voice data from atelephone 1 are AD-converted 2, voice coded 3 and then supplied to achannel encoder 4 included in the transmitter. The data, for example,from a video camera 5 or from the computer 6 are also supplied to thechannel encoder 4. The different data, for example, the voice data andthe video data can be transmitted simultaneously. The data from thechannel encoder 4 are given to a interleaver 7 and then supplied to amodulator 8 providing for a symbol mapping. The modulated data from themodulator 8 are then spread 9 and scrambled 10, which will be explainedlater on in detail. The spread and scrambled data are amplified 11, andthen transmitted over a wireless transmission path 12. It will be seenthat the interleaver 7, modulator 8, spreader 9, scrambler 10, andamplifier 11 also are included in the transmitter. On the receiving sidethe wireless transmitted data are down converted 12, A/D converted 14,descrambled 15 and despread 16. The descrambling and the despreadingwill also be explained later on in detail. The descrambled and despreaddata are de interleaved 17 and then supplied to a channel decoder 18.The channel decoder 18 outputs data to a computer 19, to a monitor 20and/or a voice decoder 21. In case of the voice data, thevoice-decoded-data 21 are D/A converted 22 and the supplied to a handset23.

With reference to FIG. 2, particularly the scrambling procedureaccording to the present invention will now be explained in detail.

In FIG. 2, the communication between a base station 24 and a mobilestation 25 is shown. Particularly the downlink channel 26 from the basestation 24 to the mobile station 25 includes the transmitter shown inFIG. 1, and the uplink channel 27 from the mobile station 25 to the basestation 24 likewise includes the transmitter. The downlink channel 26and the uplink channel 27 comprise different subchannels D₁ . . . D_(N),D_(1′) . . . D_(N′). A first subset of the subchannels of the downlinkchannel 26 can for example be used for voice data and other subchannelscan be used for the simultaneous transmission of video data. The datafrom the base station 24 are channelised (spread) with differentspreading codes C_(channel 1), . . . , C_(channel N), which are mutuallyorthogonal or bi-orthogonal 28, 30. The spread data are then scrambled29, 31 with scrambling codes C_(scramble 1), . . . , C_(scramble M).According to the present invention therefore scrambling codes which aredifferent, but need not be mutually orthogonal or bi-orthogonal, areused within the same link, for example, the downlink 26. (Theorthogonality requirements are satisfied by the spreading codes.)

For the uplink 27, according to the present invention either the samescrambling codes C_(scramble 1), . . . , C_(scramble M) as in the caseof the downlink 26, or another group of scrambling codesC_(scramble 1′), . . . , C_(scramble M′) or, as generally the uplinkchannel 27 demands for the same high bit rate as the downlink channel26, even just one scrambling code can be used.

As it has already been set forth above, the downlink channel 26 or theuplink channel 27 can comprise subchannels for video and/or voicetransmission. As one aspect of the present invention, differentscrambling codes can be allocated for the scrambling of the channelsdemanding for a high bit rate, as it is the case, for example, for thetransmission of video data. For transmission of, for example, voicedata, only one scrambling code can be used.

Regarding the details of the spreading and scrambling process,particularly the modulo-2 sum operation for the scrambling at thetransmission side and the multiplying operation for the descrambling atthe reception side, the above-cited documents WO 96/05668 A1 andEP-A-565 506 are incorporated by reference. Particularly FIGS. 1 and 2in the corresponding description (page 14 to page 19) of WO 96/05668 A1are incorporated by reference.

According to the present invention the spreading codes are generated bya code tree. This technique is known from Adachi, “Tree-structuredgeneration of orthogonal spreading codes with different lengths forforward link of DS-CDMA mobile radio”, Electronic Letters, January 1997,Vol. 33, No. 1, page 27, 28, which is incorporated herewith byreference.

Orthogonal spreading codes with different lengths can be generated by atree-structure for orthogonal multiplexing of forward-link code-channelsof different data rates in direct sequence code division multiple accessDS-CDMA mobile radio. Thereby codes of the same layer of the treeconstitute a set of Walsh functions and are orthogonal. Furthermore, anytwo codes of different layers of the tree structure are also orthogonalexcept for the case that one of the two codes is a mother code of theother.

As it has already been set forth in the introductory portion, when onlyone scrambling code (or long code) is used per link, there arerestrictions of the combinations of codes which can be used for theorthogonal codes (see Adachi et al.) These restrictions may prevent auser from being allocated to a certain channel. These restrictions areespecially important for high data rate users. Furthermore the highestdata rate is restricted to the shortest orthogonal code.

As according to the present invention, two or more scrambling codes areassigned to one link (one user), the following advantages are achieved:

-   -   increased flexibility in assignment of orthogonal codes since        the data rate can be split over at least two scrambling codes        and a different (longer) orthogonal code can be chosen from the        code tree (see Adachi et al), and    -   the highest data rate is increased since the data rate can be        split over at least two scrambling codes. Therefore a higher        data rate service on one link (uplink or downlink) can be        provided by using a plurality of scrambling codes within one        link. In this way the same channelisation codes (spreading        codes) can be reused and a higher data rate can be supported        because the highest data rate is restricted by the set of        channelisation codes (spreading codes) with the shortest link.

By only using two scrambling codes (M=2) per link (user), the totalnumber of available channelisation codes (spreading codes) can bedoubled and the maximum data rate can also be doubled.

FIG. 4 shows a symbolized cell distribution of a wireless transmissionsystem. One cell C₁ is surrounded by six other hexagonal cells C₂, . . ., C₇. According to the present invention, a total number of, forexample, 512 different scrambling codes can be used. To avoidinterference between adjacent cells, the total number of 512 scramblingcodes can for example be divided by 7 and each cell C₁, . . . , C₇ canbe allocated a subset of said scrambling codes. Different users withinone cell can use different scrambling codes allocated to the respectivecell.

As it has already been set forth above, according to the presentinvention one scrambling code is used in conjunction with a set ofchannelisation codes (spreading codes) depending upon the required datarate and services required. Adjacent base stations can use differentscrambling codes and every base station uses a set of scrambling codesto maintain different links in each cell.

An application of the present invention will now be explained withreference to FIG. 5. According to the state of the art, if a new userrequests, for example, a 2 Mbit/s service, the base station 24 is forcedto allocate a new scrambling code (and code tree) to support thisservice. The codes in the code tree are therefore not optimallyutilised.

To increase the flexibility of code assignment and increase the usage ofthe codes and the code tree, it is proposed to use as an option morethan one scrambling code per link.

In FIG. 5 a base station 24 is shown using two scrambling sequences(codes) 1 and 2. Shown by each scrambling code is a set of possibleservices being supported by each of the scrambling codes. In this loadsituation, if a new user 32 requests a 2 Mbit/s service, the basestation 24 has to devote a new scrambling code to support this service.

If, however, the new user 32 uses 2 (SF=4) orthogonal codes fromscrambling code 1 and 1 (SF=4) orthogonal code from scrambling code 2, a2 Mbit/s service can be supported and the codes and the code tree can bemore optimally utilised.

FIG. 6 shows another application of the present invention. According toFIG. 6 the idea according to the present invention is used to provide anincreased data rate, for example, for a WCDMA system. FIG. 6 shows thesuggested scheme for an increased data rate. To increase the data ratenormally in WCDMA one or both of the following approaches are required:

-   -   reduction of processing gain, and    -   increase of chip rate (enhanced bandwidth)

By utilizing the scheme as shown in FIG. 6 the data rate can beincreased by combining more than one scrambling code. The example showsthe data rate at 4 Mbit/s, but obviously higher rates can be achieved byusing more than one scrambling code.

What is claimed is:
 1. Transmitter for communicating data symbols over acommunication channel, the transmitter comprising: means for spreadingeach data symbol with a respective spreading code, wherein the spreadingcodes are mutually orthogonal, means for scrambling each spread symbolwith a respective scrambling code, the scrambling codes respectivelyhaving the same length as the spreading codes, and means fortransmitting said spread and scrambled symbols, wherein the means forscrambling are provided with a plurality of different scrambling codeswhich can be used simultaneously within the same link.
 2. Transmitteraccording to claim 1, characterized in that the means for scrambling canuse different scrambling codes for an uplink communication channel and adownlink communication channel, respectively.
 3. Transmitter accordingclaim 1, characterized in that the spreading codes are obtained by meansof a code tree.
 4. Transmitter according to claim 1, characterized inthat only in a downlink communication channel different scrambling codesare used, wherein in an uplink channel only one scrambling code is used.5. Transmitter according to claim 1, characterized in that the means forscrambling use different scrambling codes within the same link only forchannels demanding a high bit rate.
 6. Transmitter according to claim 5,characterized in that the means for scrambling use different scramblingcodes within the same link only video channels.
 7. Wireless transmissionsystem, comprising: means for spreading each data symbol with arespective spreading code, wherein the spreading codes are mutuallyorthogonal, means for scrambling each spread symbol with a respectivescrambling code, the scrambling codes respectively having the samelength as the spreading codes, and means for transmitting said spreadand scrambled symbols, wherein the means for scrambling are providedwith a plurality of different scrambling codes which can be usedsimultaneously within the same link, and wherein a subset of scramblingcodes is respectively allocated to a cell of the transmission system. 8.Wireless transmission system according to claim 7, characterized in thatdifferent spreading codes are allocated to adjacent cells of thetransmission system.
 9. Method for the transmission of data symbols overa communication channel, comprising the following steps: spreading eachdata symbol with a respective spreading code, wherein the spreadingcodes are mutually orthogonal, scrambling each spread symbol with arespective scrambling code, the scrambling codes respectively having thesame length as the spreading codes, and transmitting said spread andscrambled symbols, wherein the scrambling step provides a plurality ofdifferent scrambling codes which can be used simultaneously within thesame link.
 10. Method according to claim 9, characterized in that in thestep of scrambling different scrambling codes can be used for an uplinkcommunication channel and a downlink communication channel,respectively.
 11. Method according to claim 9, characterized in that thespreading codes are obtained by means of a code tree.
 12. Methodaccording to claim 9, characterized in that only in a downlinkcommunication channel different scrambling codes are used, wherein in anuplink channel only one scrambling code is used.
 13. Method according toclaim 9, characterized in that different scrambling codes within thesame link are used only for channels demanding a high bit rate. 14.Method according to claim 13, characterized in that different scramblingcodes within the same link are used only for video channels.
 15. Amethod for transmitting data symbols over an uplink or a downlink, eachlink having first and second communication channels, comprising:spreading each data symbol for the first communication channel, using aspreader unit, with an associated spreading code, thereby producing acorresponding spread data symbol for each data symbol for the firstcommunication channel in an uplink or a downlink; spreading each datasymbol for the second communication channel, using a spreader unit, withan orthogonal spreading code, orthogonal to the associated spreadingcode for the first communication channel, thereby producing acorresponding spread data symbol for each data symbol for the secondcommunication channel in the uplink or the downlink; scrambling, using ascrambling unit, each spread data symbol of the first communicationchannel with a primary scrambling code, thereby producing acorresponding scrambled symbol for each spread data symbol of the firstcommunication channel; scrambling, using a scrambling unit, each spreaddata symbol of the second communication channel with a secondaryscrambling code, thereby producing a corresponding scrambled symbol foreach spread data symbol of the second communication channel; andtransmitting, using a transmitter, said corresponding scrambled symbols,wherein the primary and secondary scrambling codes for the downlink aredifferent from each other and the primary and secondary scrambling codesfor the uplink are the same as each other, wherein a resulting data rateis spread over two or more of the scrambled codes.
 16. The methodaccording to claim 15, wherein the primary or secondary scrambling codedoes not effect a band rate of the transmission.
 17. A method fortransmitting one or more data symbols over an uplink or a downlink atdata rates, each link having a first communication channel and a secondcommunication channel, comprising: providing the one or more datasymbols to the first communication channel and the second communicationchannel in an uplink or a downlink; spreading each data symbol for thefirst channel, using a spreader unit, with a first spreading code,producing a first spread data symbol; spreading each data symbol for thesecond channel, using a spreader unit, with a second spreading code,producing a second spread data symbol, wherein the first spreading codeand the second spreading code are mutually orthogonal, scrambling, usinga scrambling unit, the first spread data symbol with a primaryscrambling code; scrambling, using a scrambling unit, the second spreaddata symbol with a secondary scrambling code; and providing, using ascrambling unit, a plurality of different scrambling codes for thecommunication channels in the uplink or the downlink, the scramblingcodes being configured simultaneously within the same link, thescrambling codes for the communication channels in the downlink aredifferent from each other when the data symbols in the downlink are of adata rate higher than a voice data rate, and the scrambling codes forthe communication channels in the downlink are the same as each otherwhen the data symbols in the downlink are of a data rate equal to orlower than the voice data rate, wherein a resulting data rate is spreadover two or more of the plurality of different scrambled codes.
 18. Themethod of transmitting according to claim 17 wherein the plurality ofdifferent scrambling codes comprise a portion of the primary scramblingcode and a portion of the secondary scrambling code.